Based on studies in mice, a transcript variant ROBO3.2 is produced from nascent ROBO3 mRNA by alternative splicing. Existence of this splicing isoform is predicted to be conserved in humans and rats. The alternative splicing results in retention of the intronic sequence between exons 26 and 27, which creates a premature stop codon. While Robo3.1 mouse mRNA is expressed in the pre-crossing and crossing commissural axons, Robo3.2 mRNA is expressed after midline crossing and thought to block midline re-crossing (Chen et al. 2008).